Here’s a good reason to remember your postal carrier at Christmas time. Apparently, he or she can tell you if the government is secretly monitoring your mail.

Federal prosecutors in Detroit say letter carrier Darlene Cry illegally tipped off a postal customer that he was the subject of a "mail cover" — a form of warrantless surveillance in which the envelope information on every card and letter received is secretly recorded by the Post Office, then passed to federal law enforcement or intelligence officials.

"From on or about April 22, 2005 thought on or about May 21, 2005, a mail cover was conducted for all mail pieces addressed to an individual residing on Lauder Street in Detroit, Michigan who was, at all times relevant to the Information, the subject of an ongoing federal criminal investigation," reads the complaint (.pdf) filed in the U.S. District Court for the Eastern District of Michigan on Friday.

On July 8th of that year, Cry "did disclose to the subject … that his mail was monitored by the Postal Service," the complaint alleges, violating a federal law against disclosing confidential government information, a misdemeanor.

Courts have ruled that Americans have no reasonable expectation of privacy in the address information on their mail, and mail covers have a long and storied history in the annals of domestic surveillance. In the 1970s, the Church Committee found that the CIA and FBI had used the mail cover program as a front to secretly open, copy and re-seal some 215,000 letters, in a single spying operation run from an office in New York.

In 2005, the Bush administration unsuccessfully lobbied Congress for expanded authority to obtain mail covers, complaining that the Postal Service’s standards for approving the surveillance were too restrictive.

Unlike other forms of surveillance, like wiretaps and pen registers, statistics on the number of mail covers performed each year are not released. In 2007, Salon reported on widespread suspicions in the civil liberties community that the secret number is rising.

It’s surprising to hear that an ordinary letter carrier would be privy to the workings of a surveillance program, even one as antiquated as mail snooping. It’s also kind of reassuring. If you notice your mailman, or mailwoman, avoiding eye contact the time you sign for a parcel, they may be trying to send you a message.